1. Field
The present disclosure relates to methods, compositions, and kits for determining the presence of a nucleic acid in a sample, including nucleic acids derived from Human papillomavirus (“HPV”).
2. Description of Related Art
Human papillomavirus (HPV) infection is the most important cause of cervical cancer, 13 types of which cause HPV-related cervical disease and cancer. Screening for oncogenic HPV DNA using molecular tests has been useful to diagnose HPV-related disease. However, current testing methods cannot precisely predict which infections may develop into cancer because most HPV infections are transient and regress and clear spontaneously. Therefore, additional biomarkers are being explored for use in reflex assays to confirm which infections will progress and require further treatment.
The progression of disease may be related to the expression of certain HPV genes. Detection of HPV mRNA may, therefore, be an additional biomarker for severe infections. Some HPV mRNA assays being developed for diagnostics detect a single type of transcript species, such as the E6 or E7 oncogenic sequences. These assays may not predict severe infections because the abundance of a single species may fluctuate due to the complex pattern of expression that occurs during the course of disease, or due to degradation of HPV from immune responses. In addition, an mRNA target may degrade after collection, or the number of infected cells in the collected specimen may be low, both of which may affect the assay result. As a solution, HPV assays designed to detect simultaneously two species of mRNAs in a ratio may be more predictive of disease than assays that detect a single mRNA species.
Additionally, HPV DNA is typically maintained as a productive infection in a circular, episomal state at 50-100 copies per cell. In this state, transcription of the HPV oncogenes E6 and E7 is tightly controlled by the E2 protein. E6 and E7 target p53 and pRb, respectively, and thus interfere with the normal cell cycle. Cells in which this transcriptional control is removed have a proliferative advantage over other cells due to their accelerated reentry into the cell cycle. Disruption or deletion of the E2 gene, as frequently occurs during integration of the virus into the host genome, removes the negative feedback on E6 and E7, activates telomerase, and derepresses hTERT expression, and thus clearly contributes to the progression of cell immortalization and ultimately, cancer progression.
The detection and characterization of specific nucleic acid sequences and sequence changes have been utilized to detect the presence of viral or bacterial nucleic acid sequences indicative of an infection, the presence of variants or alleles of mammalian genes associated with disease and cancers, and the identification of the source of nucleic acids found in forensic samples, as well as in paternity determinations. Characterization of the RNA species involved in normal biological processes may be important to understanding various little known biological processes.
The detection and characterization of RNA (e.g., messenger RNA, transfer RNA, ribosomal RNA, small nuclear RNA, and other RNAs) is an important tool in many fields including molecular biology, toxicology, and biochemistry. Messenger RNA (mRNA) is an essential functional constituent of a cell; during the process of gene expression, the functional single strand structure of mRNA is synthesized and serves as an intermediate template for the translation process in protein synthesis. The brief existence of an mRNA molecule begins with transcription of DNA into an RNA molecule, and ultimately ends in degradation. During its life, an mRNA molecule may also be processed, edited, and transported prior to translation. Splicing is the process by which pre-mRNA is modified to remove certain stretches of non-coding sequences called introns; the stretches that remain may include protein-coding sequences and are called exons. Sometimes pre-mRNA messages may be spliced in several different ways, allowing a single transcript to encode multiple proteins.
Detection of messenger RNA (mRNA) is critical in diagnostics because it can provide viral load and gene expression information that DNA detection cannot. These factors often give clues about the progression and prognosis of a disease. The current technologies for mRNA detection present a number of problems including complexity and potential for contamination.
The most common methods of mRNA detection include Northern blot, ribonuclease protection assay (RPA), and reverse-transcriptase polymerase chain reaction (RT-PCR). However, each of these techniques, while affording some advantages in sensitivity, requires time and material demands. In addition, some techniques require amplification of the target mRNA since total mRNA represents only about 1% of the total RNA and any particular mRNA is a significantly smaller percentage.
Currently, reverse transcriptase-polymerase chain reaction (RT-PCR) is widely used to characterize RNA transcripts. However the method has the following limitations: 1) only a limited number of the specific regions can be co-amplified; 2) mutations or alternative splicing can limit the ability of specific primers to detect the RNA; and 3) it is difficult to characterize the mRNA structure in a continuous mode method.
It therefore would be useful to have materials and methods capable of determining whether the a given nucleic acid is present or absent in a sample. Additionally, it would be useful to have materials and methods capable of determining whether a gene—including the HPV E2 gene—is disrupted, deleted, or otherwise is not being expressed in a host cell.